In 2004, South Australia's fertility rate reached a near historic low of 1.68 births per woman. Since then, it has increased to its 2007 level of 1.92, the highest rate since 1975. Sustained periods of fertility well below the replacement level of 2.1 babies per woman leads to a decline in natural population growth. This, together with increasing life expectancy at birth, is one of the drivers of an ageing South Australian population. Given the potential economic impacts of an ageing population, fertility is of particular interest to policy makers.

This article examines the recent increase in South Australia's Total Fertility Rate (TFR) using data from Births, Australia (cat. no. 3301.0). The article examines fertility trends with regard to the age of mother and the relative socio-economic status of the region in which she lives. All female age groups, except for the 45 to 49 year age group, experienced an increase in fertility between 2004 and 2007. The younger age groups showed the greatest percentage increases in fertility rates but females aged 25 to 29 and 30 to 34 years had the largest absolute increase. As shown in this article, low socio-economic areas in South Australia are more likely to have higher rates of fertility in younger age groups compared to higher socio-economic areas.

REGISTERED BIRTHS

During 2007 there were 19,662 births registered in South Australia, the highest number recorded since 1993. There was a period of decline in the number of registered births in South Australia from 1993 to 2004, but after that, up to 2007, there was an increase (refer to the graph below). The increase from 2004 to 2007 coincides with the introduction of the Federal Government's Baby Bonus (introduced on 1st July 2004), which gives financial assistance to families following the birth or adoption of a baby (Family Assistance Office, 2008).

Amendments to the A New Tax System (Family Assistance) Act 1999 which took effect from 1 July 2007 require the registration of, or application for registration of, the birth of a child as a condition for applying for the Baby Bonus. This may have affected the number of births registered in 2007 as there is usually an interval between the occurrence and registration of a birth (ABS, 2007a).

Registered Births, South Australia

Median Age of Parents

The median age of South Australian mothers at confinement has increased from 25.4 years in 1975 to 30.3 years in 2007. There was a consistent increase in the median age of both mothers at confinement and fathers over the period from 1975 to 2004, but a notable drop, as depicted in the graph below, was observed in 2005. The median age of mothers fell from 30.8 in 2004 to 30.1 in 2005. This is the only recorded period where the median age of South Australian mothers has fallen. This coincides with the time at which the fertility rate began to increase in South Australia, and as shown later in this article, it was the age groups under 30 years of age which experienced the biggest percentage increase in fertility at this time.

Median Age of Parents at Confinement, South Australia

Total Fertility Rate

The Total Fertility Rate (TFR) represents the average number of babies that a woman could expect to bear during her reproductive lifetime, assuming that current age-specific fertility rates apply. South Australia's TFR has increased over the last three years from 1.68 births per woman in 2004 to 1.92 in 2007. This is the highest level since 1975.

At the height of the 'baby boom' in 1961 South Australia's TFR was 3.75 babies per woman. During the later 1960's and early 1970's, the TFR declined markedly as the oral contraceptive pill became available. The re-interpretation of abortion law also had an impact on women's ability to control their fertility (Carmichael, 1998). The current and historical fertility trends shown in South Australia are similar to those experienced nationally.

Total Fertility Rate (a), Australia and South Australia

Age-Specific Fertility Rates

Age-specific fertility rates for all age groups in South Australia, except for the 45 to 49 year age group, increased between 2004 and 2007 (refer to the table below). During this period, the greatest percentage increases occurred in the 15 to 19 and 20 to 24 year age groups while the 25 to 29 and 30 to 34 year age groups had the greatest absolute increase. All of the age groups under 30 years of age reversed the downward trend that was apparent in their fertility rates prior to 2004. For example, the teenage fertility rate decreased from 45.8 babies per 1,000 women in 1971 to 13.5 babies per 1,000 women in 2004 before increasing to 17.5 babies per 1,000 women in 2007.

While the younger age groups showed the greatest increases in fertility rates between 2004 and 2007, they showed the greatest decreases between 1971 and 2004. Women aged 20-24 years have experienced the greatest decrease, with the fertility rate falling from 172.6 babies per 1,000 women in 1971 to 48.3 babies per 1,000 women in 2004.

As shown previously in this article, the median age of mothers at confinement increased from 25.4 years in 1975 to 30.3 years in 2007. The shift to an older age-specific fertility pattern can be seen in the graph below. From 1971 to 1998, women aged 25-29 years had the highest fertility rates in South Australia. After 1999, the peak fertility age group was 30-34 years.

Since 2002, the fertility rate of South Australian women aged 35-39 years has been similar to that for women aged 20-24 years. Historically, women aged 20-24 years had significantly higher fertility rates than women aged 35-39 years.

Age-Specific Fertility Rates (a), South Australia

Number of Births by Socio-Economic Status

Using the Socio-Economic Indexes for Areas (SEIFA), it is possible to analyse the number of births in South Australia by the relative socio-economic status of Statistical Local Areas where the mother resides at the time of birth. SEIFA indexes are summary measures of a number of variables that represent different aspects of relative socio-economic advantage and/or disadvantage in a geographic area. Based on international research and also on information collected in the Census, the ABS broadly defines relative socio-economic advantage and disadvantage in terms of people's access to material and social resources, and their ability to participate in society (ABS, 2006).

Of all the births to teenage mothers in South Australia between 2005 and 2007, 41.6% were to mothers who resided in the most disadvantaged quintile of the SEIFA Index of Relative Advantage and Disadvantage (refer to graph below). This was despite the fact that only 18.2% of females aged 15 to 19 actually lived in such areas in 2006 (ABS, 2007b). Conversely, 7.3% of all births to teenage mothers were to mothers who resided in the most advantaged quintile, even though 28.7% of females aged 15 to 19 lived in such areas.

As the age of the mother increased, the proportion of births in the most disadvantaged areas generally decreased. For example, only 13% of births to mothers aged 35 to 39 were to mothers who resided in the most disadvantaged quintile of the SEIFA index, while 17.4% of females in this age group lived in such areas (ABS, 2007b).

Proportion of All Births in Age-Group, 2005-2007 (a), South Australia

For the period 2005 to 2007, 20.0% of all births in South Australia were to mothers who lived in the most disadvantaged quintile of the SEIFA Index of Relative Advantage and Disadvantage, virtually unchanged from 20.1% for the period 2002 to 2004.

Proportion of All Births by SEIFA Quintiles (a), South Australia

CONCLUSION

South Australia's Total Fertility Rate increased from 1.68 births per woman in 2004 to 1.92 in 2007. All age groups, except for the 45 to 49 year age group, showed an increase in fertility between 2004 and 2007. The younger age groups had the greatest percentage increases in fertility rates and females aged 25 to 29 and 30 to 34 years had the largest absolute increase.

While the younger age groups have had the greatest increase in fertility between 2004 and 2007, they have had the greatest decrease in fertility between 1971 and 2007. The median age of women giving birth has increased from 25.4 years in 1975 to 30.3 years in 2007, with the 30-34 year age group now having the highest fertility rates in South Australia.

As shown in this article, low socio-economic areas are more likely to have higher rates of fertility in younger age groups, with over 40% of all teenage births between 2005 and 2007 occurring in the most disadvantaged areas of South Australia.

Carmichael G, 1998, Things Ain't What They Used to Be! Demography, Mental Cohorts, Mortality and Values in Post-war Australia, Presidential address, Journal of the Australian Population Association, Vol 15, No 2.

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